Umarov said in a statement posted on Monday that he ordered the airport bombing and many more such attacks will follow if Russia does not allow the Caucasus to become an independent Islamic state governed by Sharia law.

In another video released over the weekend, he appeared with a young man whom he said was being sent to Moscow on a suicide mission.

Umarov has claimed responsibility for an array of terrorist attacks, including last year's double suicide bombing of the Moscow subway system which killed 40 people. He is seen more as an ideological than a military figure, as many militant cells operate autonomously and shun centralised command.

Some observers have questioned Umarov's claim. Ben West, an analyst at Stratfor, a global intelligence analysis company, said in a written comment that Umarov could have claimed the attack to boost his profile after falling out with other rebel leaders last autumn.

Chechen rebels have fought two separatist wars against Russian forces since 1994. Major offensives in the second war died down about a decade ago, but the Islamic insurgency has spread across neighbouring North Caucasus provinces, stoked by poverty, official corruption and abuses against civilians by security forces.